The overall goal of the proposed research program is to gain knowledge about basic mechanisms and evolution of acoustic communication systems in vertebrates, using frogs as a model system. Frogs do not rely on acoustic experience to produce or to recognize species-specific communication signals, and they can be studied using genetic-developmental and neurophysiological techniques that would be difficult or impossible to apply in higher vertebrates. This research will provide insights into fundamental mechanisms of the neural processing and evolution of complex, temporal patterns of the acoustical signaling that mediates sexual responsiveness and mate recognition. Analogous sounds form basic elements of the human speech code that are recognized by human infants with little prior exposure to human language. The proposed research will thus address issues concerning the biological bases of the inborn neural specificity for species-typical patterns that are later modified in higher animals by experience. The normal development and maintenance of speech communication have an obvious and critical bearing on human mental health. The main study species will be treefrogs that communicate by stereotyped signals in which the most important biologically relevant information is encoded in temporal patterns. These include the repetition rate and shape of sound pulses, which identify the species and are also geographically specific, and call duration and repetition rate, which are used by females for intraspecific mate choice. Behavioral studies will determine the relative importance of these temporal properties in determining the overall effectiveness of a signal in eliciting phonotactic responses from female frogs. The neurophysiological methodology will include recordings of neural responses in freely moving, behaving animals. The evolutionary aspects of acoustic communication by temporal codes will be addressed by studying the selective and genetic bases of geographical variation in both male signals and female selectivity for these signals. Finally, behavioral, anatomical and neurophysiological studies of artificially produced polyploid frogs will provide insights into the possible mechanisms that gave rise to different temporal codes and parallel selectivity for those codes in a pair of cryptic diploid-tetraploid treefrog species. The release time made possible by an RSA will permit the P.I. to devote nearly full time effort to basic research, to lead a research team composed of undergraduates, graduate students and postdoctoral researchers, and to form collaborative arrangements with other neuroethologists. The Division of Biological Sciences of the University of Missouri has a strong commitment to basic research in neurobiology and neuroethology that is manifest in recent and planned recruitment of new faculty in this area.